This invention relates to equipment for drilling and producing from a subsea oil or gas well and is particularly directed to an improvement in the connection between the various pieces of equipment to prevent the intrusion of sea water into the equipment's hydraulic control conduits (lines) and to prevent hydraulic lock of certain valve actuators (as a fail-safe feature) in the event of an emergency or accidental disconnection of various pieces of equipment.
This invention will first be described as part of a connector and mandrel application used to connect the various pieces of equipment together and then later the invention will be described as part of a tree cap or running tool application which intrusion of sea water and hydraulic lock are also problems. Thus, by way of example, the equipment used to produce from a subsea well conventionally includes a completion tree which is connected to the wellhead located at or near the mudline, a control module containing various actuators for controlling valves located on the completion tree and within the well itself, and, finally, a tree cap having a plurality of hydraulic control lines for connecting the various actuators in the control module, the tree, and in the well itself to a rig located at the water level. From time to time a running tool will also be used to service the well, if need be.
The connectors used in connecting the tree to the wellhead, the control module to the tree, etc., each have hydraulic control lines extending therethrough which mate with similar hydraulic control lines in a member such as a mandrel on the tree, control module, etc., so that the fluid under pressure may be directed to the various valve actuators. Thus, all control lines are connected between each piece of equipment and between the equipment and the well via the connector and a mandrel.
These connectors have a cone shaped surface which will mate with a complementary cone shaped surface on the mandrel, and suitable sealing devices carried by the connector and positioned to seal the control lines at their mating surfaces, sometimes called the "member interface," to prevent leakage of the fluid along the member interface. A typical cone seal connector with its cone seal is illustrated, described, and claimed in the Pfeifler U.S. Pat. No. 4,440,423 to which reference be made for more details. See also the improved cone seal as disclosed and claimed in the U.S. patent application Ser. No. 727,658, filed April 26, 1985 by James Albert and James Dean, which also may be used with this invention.
For the purposes of this description, the connector with its cone surface may be referred to as the "female member" or "movable member" to indicate the fact that normally the connector is lowered and connected onto the mandrel which has a complementary cone surface which may be referred to as the "male member" or "semi-permanent member." These members are also referred to as a "cap member" and "head member", respectively, in the Pfeifler patent.
It is to be understood that while this invention is described in connection with well production equipment, this invention is also usable with well drilling equipment.
The problem that arises and the solution to which this invention is directed involves an emergency or accidental disconnection of one of the members. Such a disconnection would normally allow the intrusion of sea water into the hydraulic control lines thereby contaminating the fluid. To solve this problem in a connector and mandrel interconnection, one-way check valves are located at the member interface. These one-way check valves are mechanically opened for the flow of fluid pressure and are spring actuated to close in the event of disconnection of the connector, thereby preventing the intrusion of sea water into the hydraulic lines. According to this invention, these one-way check valves are formed in such a manner that only a minute amount of sea water is allowed to intrude.
There is another problem, however, the solution to which this invention is also directed. That is the problem of hydraulic lock that may occur upon the emergency or accidental disconnection of the connector and closing of the one-way check valves. For example, in the event that one of the control valves regulating the flow of oil from the well has been hydraulically actuated to an open condition by the rig operator. Upon disconnection, this control valve will be locked open by the function of the one-way check valve system of the disconnected connector. This could be catastrophic because the control valve is locked open and out of the control of the rig actuator. To solve this problem, a second one-way valve, preferably located in one of the one-way check valves, will vent the high pressure fluid holding the control valve locked open to sea water thereby allowing the locked control valve to close and shut off the flow of fluid from the well.
It can be seen, therefore, that it is an object of this invention to provide a system for subsea control lines to prevent any water intrusion and with a fail-safe close feature in the event of an accidental or emergency disconnection of various subsea equipment.